: Thread coupling for drill string elements for percussion drilling. The thread coupling comprises a first drill string element (1) provided with a sleeve formed part (2) having an internal thread (3) and a free end (4) for cooperation with a second drill string element (6) provided with a stop face (10) and a spigot (7) with an external thread (8). The free end (4) and the stop face (10) are hardened during manufacturing, preferably through case-hardening, to a depth of at least 2 mm. Furthermore, thesleeve formed part (2) and the spigot (7) are given such dimensions during manufacturing that a bottom play (A) of 1.1-2.0 mm, preferably 1.1-1.5 mm, is obtained when coupling newly made drill string elements.
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